To expand on stustustugoo' reply, here are some examples of how you would use the word as a noun and in its' adjectival form, smutty:
I sent my mate a smutty postcard
Those top shelf magazines are just smut
What you're thinking is pure smut
That's a smutty suggestion
You wouldn't use it in the way you did (I also did some smut today) that's unless you're trying to start a new, cool expression, like saying I did some dope today. Hope that helps.
And, like, hell! I'm not the greatest at english grammar, so who am I to be picky, I make up words and expressions all the time.